The use of security documents which must be able to be authenticated to confirm their value has become increasingly common as a part of daily life in modern society. For example, banknotes and other currency security documents such as traveller's cheques and bonds for example are used on a daily basis by billions of people, and must be able to be authenticated by users in order to avoid losses due to fraud and counterfeiting. Identity security documents such as passports, driver's licenses and identity cards for example are in widespread use and must be able to be accurately authenticated to verify the identity of the individual presenting the document. Similarly, other valuable security documents such as credit cards, cheques and share certificates for example are exchanged in everyday commerce and must be able to be authenticated in order to detect and avoid fraud. Accordingly, security features have been developed to be used in connection with security documents for the purpose of enabling the authentication of the document by users, as well as by law enforcement and government authorities.
One type of security feature known for use in security documents to make their copying more difficult, and the detection of copies more likely include passive physical features which are incorporated into the security document itself and visible to an unaided user. Such features include watermarks, embossings, metallic threads, holograms, metallized foils and other similar distinct and visible features which have been commonly implemented in banknotes, passports and cheques, for example. Unfortunately the development of advanced and inexpensive printing and copying technologies has made it possible for forgers to easily and convincingly reproduce many of these conventional visual authentication features, which have led to the failure of such known features to assure authenticity of security documents.
A further type of known authentication features incorporated in security documents includes magnetically, optically or radio frequency readable information encoded on the security document for detection and reading with an external device. Such features include magnetically readable strips on passports and credit cards, optically readable features such as microprinting or UV-fluorescing inks, and RFID transmitters, which may all be read or authenticated only with the use of an external reading and/or authentication device. Unfortunately, technological advances have also made such encoded security features relatively easy for forgers to copy, such as by duplicating magnetic card strips, and inexpensive high resolution microprinters, for example, leading to increased frequency of serious fraud and counterfeiting of security documents relying on such known encoded or machine-readable security features. Additionally, reliance on such known encoded or machine-readable security features that require an external device for authentication prevents an unaided user from being able to determine whether a security document is authentic or not.
Accordingly, there is still a need to develop alternative designs and features for security documents that enable their authentication by multiple types of users and for multiple types of uses, and that are not able to be easily or inexpensively reproduced by forgers or counterfeiters.